1. Field of the Invention
This application claims the benefit of Korean Patent Application No. 10-2013-0001623, filed on Jan. 7, 2013, which is hereby incorporated by reference as if fully set forth herein. The embodiments of the invention relate to an optical controller, and more particularly, an optical controller containing electrophoretic fluid. Although embodiments of the invention are suitable for a wide scope of applications, it is particularly suitable for an electrophoretic display device having a partition structure.
2. Discussion of the Related Art
In general, an electrophoretic fluid has pigment particles suspended in a clear dielectric fluid or a colored transmissive dielectric fluid. Each of the pigment particles has a permanent charge. An electrophoretic device typically includes the electrophoretic fluid between spaced-apart plate-like electrodes. One of the electrodes is typically transparent. The other electrode may have a smaller width than the transparent electrode and be disposed on a lower substrate. When a voltage is applied across the two electrodes, the pigment particles collect at the electrode of polarity opposite that of the charge on the pigment particles. The pigment particles are typically collected at the electrode with a smaller width or at the bottom of a shallow reservoir. Thus, a color of light passing through the electrophoretic device will be the color of the dielectric fluid through which the light passes. A subsequent reversal of the voltage polarity on the electrodes causes the particles to disperse back into the dielectric fluid such that the color is like that of the pigment particles plate.
An electrophoretic display is flat panel display device that can include thousands of electrophoretic devices. Each of the electrophoretic devices should have the same amount of pigment particles and dielectric fluid such that each of the electrophoretic devices have the same performance in response to voltages on the electrodes of the electrophoretic devices. Because the pigment particles are in a fluid, the pigment particles may undesirably move within a display due to gravity such that some electrophoretic devices have significantly more pigment particles than other electrophoretic devices in the display. To prevent undesired movement, such as sedimentation, of the pigment particles within a display, partitions divide the display into cells containing electrophoretic fluid for one or more electrophoretic devices. However, there are difficulties in forming electrophoretic displays with partition structures.
FIG. 1 shows a flow chart for a method of forming an electrophoretic display by continuously dispersing electrophoretic fluid and sealant according to the prior art. As shown in FIG. 1, a method 1 of forming an electrophoretic display according to the prior art includes forming a lower electrode on a lower substrate 2. Then, the method 1 continues by forming a plurality of divided regions on the lower substrate 3. Subsequently, an electrophoretic fluid is continuously dispensed into the divided regions 4.
FIG. 2a illustrates an apparatus and method for continuously dispersing electrophoretic fluid prior to bonding substrates for an electrophoretic display according to the prior art. As shown in FIG. 2a, lower electrodes 11 are formed on a lower substrate 10. The lower substrate 10 is divided into regions by partitions 12. An electrophoretic fluid dispenser 13 moves in a direction D and continuously dispenses electrophoretic fluid 14 onto the lower substrate between the partitions 12 and onto the partitions 12.
As shown in FIG. 1, the method 1 includes continuously dispensing a sealing layer onto electrophoretic fluid 5. Then, the sealing layer is cured on the electrophoretic fluid 6. The curing can be done using ultraviolet light.
FIG. 2b illustrates an apparatus and method for continuously dispersing sealant prior to bonding substrates for an electrophoretic display according to the prior art. As shown in FIG. 2b, a sealing dispenser 15 moves in a direction D and continuously dispenses a sealing layer 16 onto electrophoretic fluid 14. The sealing layer 16 is on the electrophoretic fluid 14 between the partitions 12 as well as the electrophoretic fluid 14 on top of the partitions 12. The sealing layer 16 seals the electrophoretic fluid 14 between the partitions 12 and prevents migration of both the pigment particles and dielectric fluid of the electrophoretic fluid 14.
As shown in FIG. 1, the method 1 includes forming an upper electrode on an upper substrate 7. The upper electrode can be a sputter deposited indium tin oxide. Then, the method 1 includes forming an adhesive layer on the upper substrate 8. The adhesive layer can be an applied double-sided adhesive or a sprayed on adhesive. After the upper and lower substrates are formed, the method 1 includes positioning the adhesive layer of the upper substrate onto the cured sealing layer of the lower substrate to bond the upper and lower substrates together 9.
FIG. 2c illustrates a cross-sectional view of bonding substrates for an electrophoretic display according to the prior art. As shown in FIG. 2c, an upper electrode 18 is formed on an upper substrate 17. The upper substrate 18 is transparent. An adhesive layer 19 is provided on the upper electrode 18. The adhesive layer 19 is positioned to be lowered onto the cured sealing layer 16 to bond the upper substrate 17 and lower substrate 10 together using the adhesive layer 19.
FIG. 2d illustrates a cross-sectional view of an electrophoretic display according to the prior art. As shown in FIG. 2d, the divided regions between the partitions 12 an electrophoretic display according to the prior art may not be uniformly filled with electrophoretic fluid 14. Non-uniformity in filling along with varying sizes of air gaps between the partitions can cause variations in performance amongst an array of pixels in an electrophoretic display device. The ultraviolet curing of sealant on the electrophoretic fluid can cause a chemical reaction between the sealing layer and the pigments particles, which randomly degrades the individual performance characteristics of pigment particles for electrophoresis amongst the array of pixels in an electrophoretic display device. Further, the presence of the sealing layer together with the electrophoretic fluid on top of the partitions can cause the appearance of point defects on the display due varying thicknesses of combinations of sealing layer together with the electrophoretic fluid.